Repair Bond Strength of Aged Bulk-Fill Composites: Influence of Different Primers and Direction of Debonding Stress

European Journal of Prosthodontics and Restorative Dentistry (2025) 33, 339–345

Bulk-fill Resin Composite Adhesive Interface Stability Shear Bond Strength (SBS) Micro-tensile Bond Strength (μTBS)

Pekka Ahlholm*
(DDS, PhD)

Frode Staxrud §

(DDS, PhD, Senior scientist)

Kirsi Sipilä ‡ ^

(DDS, PhD, Professor)

Pekka Vallittu † Δ

(DDS, PhD, CDT, Professor)

Address for Correspondence
Pekka Ahlholm*
Email: ahlholm.pekka@gmail.com
* Department of Oral and Maxillofacial Diseases,
Helsinki University Hospital, Helsinki, Finland
§

Nordic Institute of Dental Materials, NIOM, Oslo,
Norway

‡

Research Unit of Population Health, Faculty of
Medicine, University of Oulu, Oulu, Finland

^ Oral and Maxillofacial Department, Medical
Research Center Oulu, Oulu University Hospital,
Oulu, Finland
†

Department of Biomaterials Science and Turku
Clinical Biomaterials Centre – TCBC Institute of
Dentistry, University of Turku, Finland

Δ

Welfare District of South-West Finland,
Lemminkäisenkatu 2, 20520 Turku, Finland

Received: 16.04.2025
Accepted: 06.07.2025

Repair Bond Strength of
Aged Bulk-Fill Composites:
Influence of Different
Primers and Direction of
Debonding Stress

Objective: This study aimed to assess the hydrolytic stability of the adhesive interface between repaired bulk-fill and bulk-fill resin composites after 12 months of water storage. Materials and Methods: Bulk-fill resin composite specimens were bonded to smooth substrate surfaces using three different primer/bonding systems. A total of 35 specimens were prepared for shear bond strength (SBS) testing, and 30 specimens for micro-tensile bond strength (μTBS) testing. The specimens were aged in water at 37°C for 12 months, after which SBS and μTBS were evaluated. Results: The mean SBS ranged from 6.0 to 14.9 MPa, with the highest values observed for the Ceramic primer. The mean μTBS ranged from 0 to 7.8 MPa, with the Composite primer yielding the highest values. Both primers outperformed the three-step etch-and-rinse adhesive in terms of bond strength. Conclusions: The Ceramic primer (containing silane) and the Composite primer exhibited superior adhesive performance compared to the three-step etch-and-rinse adhesive, demonstrating better long-term bond stability. Clinical Relevance: The findings suggest that using Ceramic or Composite primers can enhance the durability of repaired bulk-fill composite restorations, improving adhesive stability and long-term clinical outcomes.

Resin-based composites have become the material of choice for direct dental restorations in modern restorative dentistry, particularly in developed countries1. Bulk-fill resin composites represent a recent innovation designed to optimize and expedite the placement of large posterior restorations, allowing increments of 4 mm or greater to be applied in a single layer2. These composites contain larger filler particles compared to conventional composites3. Furthermore, the monomer composition varies, with Bis-GMA often reduced or substituted by alternative monomers such as Bis-EMA, TEGDMA, EBPDMA, and UDMA4. The primary objective of bulk-fill composites is to minimize technique sensitivity for clinicians, enabling complete cavity fills in a single increment and thereby reducing the risk of voids within the restoration. This approach streamlines the restorative procedure5. With increased use of bulk-fill materials, complications such as fractures have become more prevalent. A contemporary method to address fractured direct restorations involves repairing them with new composite materials6. In this procedure, the new material is bonded to the existing

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